Increasing and Decreasing Functions

Hi, I am stuck on this problem, the instructions indicate to find the intervals of increase and decrease for the given function.

h(u) = square root of 9-u^2 The square root is over the entire term.

We were told to differentiate first, and then to factor to find the zeros. When I try to differentiate I am getting 3-(1/2)X^-(3/2) This doesn't look right so I need some clarification as to whether I am differentiating correctly.

BTW The final answer should be:

h(u) is increasing for -3< u < 0

h(u) is decreasing for 0< u < 3